1. Field of the Invention
The present invention relates to a method and apparatus for controlling the travel speed of a vehicle, in which the distance and relative speed of objects located in front of the vehicle are measured and the vehicle travel speed is regulated according to a set vehicle travel speed in a speed control mode and according to a predetermined set distance to a preceding vehicle in a distance control mode.
2. Prior Art
Processes and apparatuses of this type are known and designated xe2x80x9cadapative vehicle travel speed controllerxe2x80x9d and with the abbreviation xe2x80x9cACCxe2x80x9d, which means adaptive cruise control and are described, for example, in the article entitled xe2x80x9cAdaptive Cruise Control-System aspects and Development Trendsxe2x80x9d of Winner, Witte, et al., published in SAE 96, Detroit, 26.-29., February 1966, paper no. 96 10 10. Special aspects of this type of system are described in DE 196 27 727, DE 196 37 245 and DE 196 40 694.
For measurement of the distance and relative speed of one or more preceding vehicles a radar-based system or infrared-based system is provided in a known apparatus. The known radar-based system however not only detects the preceding vehicles, but also stationary objects, such as traffic signs and the like, which are detected by it. The relative speed of the stationary objects agrees with the actual speed of the vehicle that is known to the control system up to the sign. These stationary objects are however generally ignored in the distance regulation method, because they are not normally in the road or not in the travel path of the controlled vehicle. They are also ignored because the responsibility to avoid collisions with this sort of obstacle is left to the awareness of the driver for safety reasons in these systems, when this exceptional case arises.
In DE 197 57 062 A a situation is described in which a stationary obstacle is found on the road in front of the preceding vehicle and the preceding vehicle travels out from its line of travel in order to avoid this obstacle. Normally this has the consequence that the control system, which can no longer detect the preceding vehicle shifts from the distance control mode to the speed control mode and accelerates the vehicle to the set speed value originally set by the driver. The driver could thus be irritated because of that change and his or her comfort and safety could be impaired Thus the vehicle reacts inadequately in this situation, namely with an acceleration, although a slowing of the vehicle would be appropriate, considering the presence of the obstacle. For these reasons according to the above-named publication under these special conditions, thus during a change from the distance control mode to the speed control mode, the detected stationary object should be considered in this exceptional situation. Under this exceptional condition the inappropriate acceleration of the vehicle should be suppressed or a delay of the vehicle should be initiated. Since the described situation occurs primarily in city traffic, also at moderate speeds, the stationary objects should be considered only under the condition that the actual vehicle travel speed and also the distance to the stationary object are both below respective predetermined threshold values.
Of course in many cases an unsuitable and irritating reaction for the driver of the vehicle can be avoided, however situations can still occur, in which this known system reacts in an implausible and irritating manner for the driver. An example of one such situation would be the case in which the shift from the distance control mode to the speed control mode has already occurred earlier and the vehicle is still in an acceleration phase, during which the resting object is first located. Another example would be the situation in which the preceding vehicle passes an object that only partially extends into the travel path without leaving its travel path and the locating range of the radar system and then, after it passes the stationary object, accelerates again. In this case the system would remain in the distance control mode and the vehicle would accelerate, although it has not yet passed the stationary object. An additional example is travel path or route change to a new path in which a stationary object is found. Several known ACC system have been designed so that the driver can temporarily put the speed control out of action and the system under certain circumstances, for example after a predetermined delay time, automatically shift back into the control mode. Also under these circumstances an acceleration process takes place, which would be perceived as unsuitable or irritating considering the presence of the stationary object.
As reported by passengers in motor vehicles, many persons experience considerable discomfort, if a human driverxe2x80x94or an automatic systemxe2x80x94does not react in a concrete traffic situation, as they themselves would react to it. The avoidance of situations, in which an ACC system reacts implausibly or inappropriately, is a factor, which should not be underestimated in evaluating these systems.
It is an object of the present invention to provide a method of the above-described kind for regulating the travel speed of a vehicle, which guides or conducts the vehicle in a greater variety of different vehicle travel situations in a suitable manner and/or behaves in such a manner as to increase vehicle travel safety.
It is also an object of the present invention to provide an apparatus for performing the inventive method for regulating the travel speed of the vehicle, so that the vehicle travels in a greater variety of different vehicle travel situations in an appropriate manner and/or behaves in a safer manner.
These objects and others, which will be made more apparent hereinafter, are attained in a method for controlling travel speed of a vehicle, in which the distance and relative speed of objects located in front of the vehicle, including preceding vehicles, are measured, the vehicle travel speed is controlled according to a set speed given by the driver in a speed control mode and according to a set distance to a preceding vehicle in a distance control mode and under certain circumstances, when a stationary object is detected in the path of the vehicle, the vehicle reacts so that the acceleration of the vehicle is limited.
According to the invention the reaction of the vehicle limiting its acceleration is started when a stationary object is detected in the path of the vehicle, but the extent or strength of the limitation of the acceleration varies according to an analysis of relevance of the stationary object as an obstacle for the controlled vehicle, in particular according to a calculated relevance value for the stationary object as an obstacle for the controlled vehicle.
According to the invention the apparatus reacts to objects in the path of the traveling vehicle not only during a change from the distance control mode to the speed control mode, but also within the distance control mode and within the speed control mode. Overreaction of the apparatus to the stationary object causing discomfort or danger is avoided by a quantitative analysis of the relevance of this type of stationary object as an obstacle for the vehicle. An adjustment of the extent or strength of the reaction limiting acceleration of the vehicle takes place with the aid of the analysis results.
Different criteria may be set up for calculation of the relevance value of a stationary object detected in front of the vehicle as an obstacle for the vehicle. In an especially preferred embodiment of the invention these criteria include the distance of the object from the controlled vehicle (relevance-reducing), the lateral displacement of the object from the predicted center of the vehicle travel path (relevance-reducing) and the length of the time interval, within which the object is located in the travel-path (relevance-increasing). The tendency for approximate transverse motion of the object (which is still detected as xe2x80x9crestingxe2x80x9d because of a nearly zero relative speed component in the travel direction) could be considered. In addition, the decrease of radar echo intensity as the vehicle approaches the object, as occurs to some extent with smaller reflecting objects in the vehicle travel path or in the plane of travel could be considered.
The adjusting or grading of the reaction of the vehicle to a stationary object in its vicinity depends on its relevance, which is evaluated with the aid of these criteria. As a result discomfort does not occur when the stationary object is far removed from the vehicle travel path or in the vehicle travel path for only a short time. A strong reaction only occurs for those objects, which are detected as in or near the center of the vehicle travel path for a significant length of time and thus appear as an obstacle.
The gentlest reaction to the stationary object arises in a preferred embodiment in which only the rate of increase of the acceleration, not the acceleration of the vehicle itself, is limited. A xe2x80x9cback-typexe2x80x9d acceleration of the vehicle occurs during this adaptive control so that the discomfort phenomenon may be avoided before the driver slows the vehicle because of the detected obstacle. A stronger reaction, which can be used with the same or also with a higher relevance threshold, limits the vehicle acceleration to a certain maximum value. The maximum value depends preferably on the analysis of the relevance and in an extreme case can be negative, so that the vehicle is braked. In this connection also an engagement of the braking system is conceivable to actively brake the vehicle automatically.
Other advantageous features of preferred embodiments are described in the following description and claims.